The present invention relates to vectorscopes, and more particularly to vectorscope automatic burst positioning for rotating the display of a vectorscope to the correct graticule location.
An important instrument in the measuring of the characteristics of a color video signal is a vectorscope. A vectorscope is a specialized oscilloscope that demodulates the color video signal and presents a display of R-Y versus B-Y, i.e., the two chrominance components that contain the color information within the color video signal. The angle and magnitude of the displayed vectors are related respectively to hue and saturation. To properly align the vector display on the vectorscope a vector representing a burst signal portion of the color video signal is adjusted to be parallel to the horizontal axis of the display. In prior art vectorscopes, such as the 1700 Series manufactured by Tektronix, Inc. of Beaverton, Oreg., United States of America, the adjustment of the vector display is performed by manually manipulating a front panel knob and observing the vector display. The manipulation of the front panel knob provides a signal to a phase shifter within the vectorscope that affects the phase of a regenerated subcarrier signal derived from the burst signal portion of the color video signal As the phase is changed, the vector display rotates until the burst signal vector is aligned with the horizontal axis. Since the graticule for some vectorscopes includes an angular offset from the horizontal graticule, alignment of the burst signal vector provides for ease in determining subcarrier to horizontal sync (SCH) phase errors.
What is desired is a method of rotating the vector display automatically to properly align the vector display with the display graticule to make the vectorscope easier to use and to save user time.